A ‘clicked’ macrocyclic probe incorporating Binol as the signalling unit for the chiroptical sensing of anions

We describe a macrocyclic chiroptical sensor for the detection of halide anions, with the Binol moiety acting as the CD signalling unit. The macrocycle is conveniently synthesized using CuAAC ‘click’ reactions in the cyclization step; this methodology installs 1,2,3-triazole moieties within the macrocyclic backbone, able to directionally bind anions by means of CH?X^– hydrogen bonds. ¹H NMR complexation studies in CDCl₃ reveal weak binding to halide and aliphatic carboxylate anions. Halide anions, however, when held into the macrocyclic cavity, are able to trigger a large chiroptical response originating from the steric interaction with the Binol moiety, which changes its dihedral angle, thus modulating its characteristic CD signature.     

Construction of unsymmetrical bis-urea macrocyclic host for neutral molecule and chloride-ion binding

Construction of synthetic macrocyclic host that can bind with neutral molecules and anions has potential applications in supramolecular chemistry. Herein, we have designed and synthesized blue light emitting an unsymmetrical neutral bis-urea macrocyclic host. This macrocycle can bind with neutral DMF molecule (1:1) as well as Cl⁻ ion (1:1) through noncovalent interactions. X-Ray crystal structure, ¹H NMR titrations with Job's Plot, HRMS with isotropic distribution pattern, FT-IR, and density functional theory analysis revealed the binding of bis-urea macrocyclic host with the guest molecule.     

Azulene‐Based Macrocyclic Receptors for Recognition and Sensing of Phosphate Anions

Herein we report the synthesis and detailed studies of the anion‐binding properties of two 20‐membered macrocyclic tetramide receptors: one symmetrical, containing two identical azulene‐based bisamide units, the other a hybrid, containing a dipicolinic bisamide unit and an azulene‐based bisamide unit. Analysis of the crystal structures of the macrocyclic receptors revealed their preference for adopting similar well‐preorganized bent‐sheet conformations, both as free receptors and in their complexes with anions. Studies of the optical properties of both receptors revealed abilities to selectively sense phosphate anions (H₂PO₄^?, HP₂O₇^3?), allowing for naked‐eye detection of the presence of these guests in DMSO. Binding studies in solution confirmed that the receptors bind strongly to a series of anions even in highly demanding media, such as mixtures of DMSO with water or with methanol. Comparison of the anion affinity of linear analogues with that of the macrocyclic receptors evidenced the importance of macrocyclic topology. Quantitative analysis revealed that the macrocyclic receptors are selective for H₂PO₄^? over other anions. The affinity to H₂PO₄^? seen for the symmetrical receptor, containing two azulene‐based subunits, is much higher than for the hybrid macrocycle containing both the azulene‐based and pyridine‐derived subunits. This highlights that the azulene‐based building block serves efficiently as both a binding site and a structure‐preorganizing motif.     

双吡唑桥联的大环状钯(Ⅱ)配合物的合成与结构(英)

A dipyrazol-bridged macrocyclic palladium(Ⅱ) complex [{Pd(en)}₄L₄](NO₃)₈ (en=ethylenediamine, L=3,3′,5,5′-tetramethyldipyrazol) 1 was prepared in water through a [4+4] macrocyclization of cis-(ethylenediamine)Pd(Ⅱ) nitrate and the neutral form of the dipyrazol ligand 3,3′,5,5′-tetramethyldipyrazol. This cationic palladium macrocycle is highly distorted rather than a planar macrocycle and can hold eight nitrate anions around the macrocyclic framework through both hydrogen bonding and electrostatic interactions. CCDC: 192017.     

Synthesis and anion binding properties of 1,8-disulfonamidocarbazole dipyrromethane Schiff-base macrocycle & its amine analogue

A novel 1,8-disulfonamidocarbazole-dipyrromethane Schiff-base macrocycle (1) and its amine analogue (2) were designed and synthesised, and their anion binding properties were studied via UV–vis and ¹H NMR titration spectra. The obtained results showed that a small change in the macrocyclic structure (by reducing imines into the corresponding amines) produced a remarkable impact on its binding affinity and selectivity for anions. For example, macrocycle 1 displayed a 7.9:1 F^?/H₂PO₄^? selectivity; however, its amine analogue 2 showed a 78.5:1 F^?/H₂PO₄^? selectivity.     

Formation of molecular ladder elements with macrocyclic platforms via linear bifunctional ligands

Reaction between 4-aminopyridine and a dinuclear zinc(II) component of a Robson macrocyclic ligand has resulted in the formation of a molecular ladder element motif. X-ray single crystal structural analysis indicates that two pyridine rings are assembled at the same direction of the macrocycle, which are placed in a nearly parallel way via pi-pi interactions, forming a concavity structure with a macrocyclic base. It is significantly noted that one hydrogen-bond cycle generated from hydrogen atoms of two amino groups with two perchlorate anions has sustained such an assembly of two 4-aminopyridine species to stand in a face to face pattern through a weak molecular interaction on the macrocyclic platform by one-end coordination bonding. The self-assembly of 4-carboxylic pyridine acid and the same macrocyclic component in the presence of sodium hydroxide has yielded an interesting wheel-like complex. Two macrocyclic dinuclear zinc(II) components have been linked through coordination bonding with two pyridine derivatives situated on the same direction of a macrocycle. X-ray structural results suggest that the compound has a unique sandwich-like structure consisting of two macrocyclic covers with two inversely positioned bridging pyridine carboxylic groups in the middle.     

Polyhalogenated heterocyclic compounds. Macrocycles from perfluoro-4-isopropylpyridine

Perfluoro-4-isopropylpyridine was used as a building block for the two-step synthesis of a variety of macrocyclic systems bearing pyridine sub-units which were characterised by X-ray crystallography. Electrospray mass spectrometry revealed that complexation of either cations and, unusually, anions is possible depending on the structure of the macrocycle.     

Hierarchy of hydrogen bonding in bis­(1,4,7‐trioxa‐10‐azoniacyclo­dodecane) bis­(4‐amino­benzoate) trihydrate

In the title compound, 2C₈H₁₈NO₃⁺·2C₇H₆NO₂⁻·3H₂O, proton transfer occurs from the carboxylic acid group of the 4‐amino­benzoic acid (PABA) mol­ecule to the amine group of the macrocycle, resulting in the formation of a salt‐like adduct. The anions are combined into helical chains which are further bound by the water mol­ecules into sheets. The macrocyclic cations are situated between these layers and are bound to the anions both directly and via bridging water mol­ecules. The structure exhibits a diverse system of hydrogen bonding.     

含吡啶-2,6-二酰亚胺单元的大环化合物合成及性质

在硫酸催化作用下,用前体二醛1[1,3-二(2'-甲酰苯氧基)丙烷]和前体二胺2[N,N'-(2-胺基苯基)-2,6-二甲酰亚胺吡啶]合成了[1+1]席夫碱大环化合物3,进一步还原得到饱和大环4。 用¹H NMR、IR、元素分析和质谱等技术手段对大环3和4的组成进行了表征。 采用X射线衍射仪测定了大环3 和4的晶体结构。 用UV-Vis光谱仪对大环3和4与系列阴离子的作用分别进行了考察,结果表明,饱和大环4仅对F^-有明显的选择性作用,并测定了该配位反应的配位比和平衡常数,进一步考察了大环3和4对甲醇的吸附性能。     

Construction of new [2]pseudorotaxanes by hydrogen bonding assembly of macrocyclic tetrathiolactam with amides and an ester

Thionation of a macrocyclic tetralactam gave a new macrocyclic tetrathiolactam. [2]Pseudorotaxanes constructed from the macrocycle with diamides and a diester as a neutral guest have been prepared by a facile threading process. Molecular structures and hydrogen bonding association properties of the [2]pseudorotaxanes were characterized by X-ray crystallography and ¹H NMR spectroscopy.     

Influence of charge on anion receptivity in amide-based macrocycles

Binding and structural aspects of anions with tetraamido/diquaternized diamino macrocyclic receptors containing m-xylyl, pyridine, and thiophene spacers are reported. (1)H NMR studies indicate that the quaternized receptors display higher affinities for anions compared to corresponding neutral macrocycles. The macrocycles containing pyridine spacers consistently display higher affinity for a given anion compared to those with either m-xylyl or thiophene spacers. The m-xylyl- and pyridine-containing receptors exhibit high selectivity for H(2)PO(4)(-) in DMSO-d(6) with association constants, K(a) = 1.09 × 10(4) and >10(5) M(-1), respectively, and moderate selectivity for Cl(-) with K(a) = 1.70 × 10(3) and 5.62 × 10(4) M(-1), respectively. Crystallographic studies for the Cl(-) and HSO(4)(-) complexes indicate that the m-xylyl-containing ligand is relatively elliptical in shape, with the two charges at ends of the major axis of the ellipse. The anions are hydrogen bonded with the macrocycle but are outside the ligand cavity. In the solid state, an unusual low-barrier hydrogen bond (LBHB) was discovered between two of the macrocycle's carbonyl oxygen atoms in the HSO(4)(-) complex. The pyridine-containing macrocycle folds so that the two pyridine units are face-to-face. The two I(-) ions are chelated to the two amides adjacent to a given pyridine. In the structure of the thiophene containing macrocycle with two BPh(4)(-) counterions, virtually no interaction was observed crystallographically between the macrocycle and the bulky anions.     

A Bambusuril Macrocycle that Binds Anions in Water with High Affinity and Selectivity

Synthetic receptors that function in water are important for the qualitative and quantitative detection of anions, which may act as pollutants in the environment or play important roles in biological processes. Neutral receptors are particularly appealing because they are often more selective than positively charged receptors; however, their affinity towards anions in pure water is only in range of 1–10³ L mol^?1. The anion‐templated synthesis of a water‐soluble bambusuril derivative is shown to be an outstanding receptor for various inorganic anions in pure water, with association constants of up to 10⁷ L mol^?1. Furthermore, the macrocycle discriminates between anions with unprecedented selectivity (up to 500 000‐fold). We anticipate that the combination of remarkable affinity and selectivity of this macrocycle will enable the efficient detection and isolation of diverse anions in aqueous solutions, which is not possible with current supramolecular systems.     

The unique properties observed for the unsymmetrical macrocyclic compounds with the highly distorted structure

A new class of aza-macrocycles with the highly distorted structure was found to exhibit unique properties. These macrocycles react with various lithium salts to form lithium complexes and their lithium complexation reactions depend on a substituent on the macrocyclic ring; slower rates and larger equilibrium constants were observed for the macrocycle with a bulkier substituent. The irradiation of these macrocycles by UV light was found to lead to the isomerization, and the photoisomerization rate of macrocycle with the bulky substituent was much faster. The highly distorted structure of these macrocycles makes it much easier to change the conformation of macrocyclic skeleton and these macrocycles have a variety of conformations. The factors to govern this conformational change were therefore explored. The solvent effect was examined by ¹H NMR spectroscopy, because these macrocycles have a strong intramolecular hydrogen bond in the ring. As a result, the solvent was found to have a big effect on the ¹H NMR spectra of macrocycles that could be explained in terms of the conformational change of macrocycle. This finding suggests the solvent to be an important way of controlling the conformation.     

Computational Insights into the Role of External and Local Electric Fields in Macrocyclic Chemical and Biological Systems

The investigation of the role of the electric field in systems of widespread interest employing computational techniques is an emerging area of research. The outcome of applying an oriented external electric field (OEEF) on the geometric and electronic properties of the chemically unique π-conjugated cyclic carbon ring compounds has been explored with density functional theory (DFT). Distinct changes in the structural and electronic features of such ring compounds are observed upon the application of OEEFs. Importantly, the calculations indicate that a mixed aliphatic-aromatic conjugated ring converts from a singlet to a triplet after the application of an OEEF, suggesting potential applications in optoelectronics for such molecules, without the need for photochemically induced change in the spin state. Furthermore, the influence of built-in local electric fields (LEFs) present in naturally occurring macrocyclic systems such as valinomycin has also been explored. Static and ab initio molecular dynamics (AIMD) calculations indicate that LEFs are the primary driving factor in determining the energetically favoured position of counter anions such as chloride (Cl⁻) in the potassium (K⁺) and sodium (Na⁺) coordinated valinomycin macrocycle structures: they exist inside the cage in the case of K⁺ sequestration by valinomycin and outside for Na⁺. This divergence has been proposed to be the determining factor for the selectivity of the valinomycin macrocycle for binding a K⁺ cation over Na⁺.     

Crystal structure of (5,14-methyl-7,12-dimethyl-1,4,8,11-tetraazadiiminecyclotetradecylene-N,N',N',N')nickel(II) bis(diisopropyldithiophosphate) complex.

The macrocyclic tetradentate Ni(II) compound was obtained in a reaction and determined by X-ray diffraction. The crystal structure shows that the molecule is centrosymmetric, and Ni atom located in a square planar coordination environment. The two [(iPrO)2PS2]- anions are outside the macrocycle complex to balance. The Ni-N bond lengths are in the range of 1.906(2) to 1.950(2)A.     

Anion binding with some 22- and 28-membered selenaaza macrocycles: Structural aspects and Se NMR studies

A series of macrocyclic adducts of the 22- and 28-membered selenaaza macrocycles (1 and 2, respectively) with different counter anions such as halides, sulfate, perchlorate, phosphate, trifluoroacetate and nitrate has been prepared. The adducts have been characterized by elemental analysis, IR, ¹H NMR, ⁷⁷Se NMR and ESI-MS analysis. The ⁷⁷Se NMR spectrum of the adduct (7) shows an upfield shift compared to the parent macrocycle. The bromo (5), iodo (6), sulfate (7), trifluroacetate (10) adducts of the 22-membered selenaaza macrocycle and perchlorate (16), trifluroacetate (18) adducts of the 28-membered selenaaza macrocycle have been structurally characterized. The crystal structures show extensive hydrogen bonding networks. The molecular structures of all the compounds show the macrocycle to be fully protonated except the trifluroacetate adduct of the 22-membered macrocycle (10), which is only diprotonated. The binding constants of the neutral 22-membered selenaaza macrocycle towards, fluoride, bromide, iodide and sulfate ion have been determined by the NMR titration method.     

Chiral Macrocycle‐Enabled Counteranion Trapping for Boosting Highly Efficient and Enantioselective Catalysis

The tight binding enabled by tailor‐made macrocycles can be manipulated for tuning the catalysis process. In parallel to well‐developed crown ether‐based cation‐binding catalysis, a macrocycle‐enabled counteranion trapping strategy is presented for boosting highly efficient and enantioselective catalysis. A set of bis‐diarylthiourea macrocycles containing two BINOL moieties were designed and synthesized. They possess a well‐confined chiral cavity and strong binding affinities towards disulfonate anions. Caused by the tight binding, just 1 mol % macrocycle in combination with 1 mol % ethanedisulfonic acid can promote excellent conversion and up to 99 % ee in the Friedel–Crafts reaction of indoles with imines. The acid or the macrocycle alone do not afford any reactivity. The high catalytic efficiency and excellent stereocontrol was ascribed to large, complexation‐induced acidity enhancement and tight ion‐pairing facilitated by cave‐like macrocyclic cavity.     

Helical binuclear Co complexes of pyriporphyrin analogue for sensing homochiral carboxylic acids

A hybrid macrocycle composed of two bipyridines and two dipyrrins gave biscobalt complexes of figure eight macrocycle conformation with κ²-carboxylate ligands and water ligands at the axial sites. The axial acetate ligands of the biscobalt complex are readily exchanged with carboxylates of α-hydroxyl acids and α-amino acids. The chiral center of the axial carboxylate ligands controls the helical handedness of the macrocycle as evidenced by a typical CD couplet at 550 nm. The substitution labile nature of the biscobalt complex plays a key role for helical chirality induction on the macrocycle upon co-ordination of chiral carboxylate anions.     

The use of macrocycles as electroosmotic flow modifiers in the separation of inorganic anions by capillary electrophoresis

In a novel approach to the use of macrocycles in separation systems, we report the use of macrocyclic ligands as electroosmotic flow modifiers for the separation of inorganic anions by capillary electrophoresis (CE). Inorganic anions were successfully separated through the use of 18-crown-6 or cryptand 2.2.2. as electroosmotic flow modifiers. We found that for our CE system, use of a macrocycle as the modifier resulted in better baseline stability and better efficiency than the commonly used modifier DETA. In our system, the separation efficiency and electroosmotic flow varied according to the pH of the buffer and the affinity of the macrocycle for the buffer metal cation. Results for sodium- and potassium-based buffers show that for the cryptand, pH plays a role in determining the amount of macrocycle-metal complex formed. Separations of a 12 anion standard illustrate these results. In addition, we report the effect of concentration of both macrocycle and metal ion on complex formation and resultant electroosmotic flow modification. Relationships between the macrocycle-metal complex, the buffer medium, the efficiency of separation, and the migration times of the analytes are discussed, and theoretical interpretations presented.     

6 + 6 Macrocycles derived from 2,6-diformylpyridine and trans-1,2-diaminocyclohexane

While the non-templated reaction of racemic trans-1,2-diaminocyclohexane with 2,6-diformylpyridine leads to a mixture of 2?+?2 and 4?+?4 macrocyclic imines, the reaction of the isolated 2?+?2 macrocycle with cadmium(II) chloride results in the fusion of three smaller macrocyclic units into a large 6?+?6 macrocycle. The X-ray molecular structures of the hexanuclear cadmium complex of this macrocycle as well as the derived 6?+?6 protonated amine reveal multiply folded macrocycles that adopt container-type conformations.